Phenol and acetone have been mutually prepared by the cumene basic process for almost forty (40) years as disclosed in U.S. Pat. No. 4,567,304, hereinafter incorporated by reference. Cumene is peroxidized to give cumene hydroperoxide which is then acid cleaved to provide phenol and acetone. The phenol and acetone are then split by a distillation column via their separate boiling points followed by various purification procedures for both the phenol and acetone. Obviously by-products are formed as well as the desired products of phenol and acetone. Particularly detrimental to phenol quality are color embodying impurities generally of the carbonyl family. Of particular concern are the alpha-hydroxycarbonyls as typified by the main contaminant, alpha-hydroxyacetone. These particular compounds are deleterious to the quality of phenol, particularly in the coloring of end products from phenol. One of the quality tests utilized is the sulfonation color test wherein very small amounts of alpha-hydroxyacetone can provide very poor product implications to phenol. It is therefore very important to remove as much of these carbonyl contaminants from the phenol stream as possible.
This problem has been well recognized in the past as shown by a number of issued patents which have attempted to remove the carbonyl contaminants by expensive and elaborate processes. For example, Great Britain 1,108,584 removes the carbonyl contaminants from the phenol by contacting the carbonyl compound-contaminated phenol composition with a cation exchange resin such as the sulfuric, sulfonic, phosphoric and phosphonic substituted polystyrene cation exchange resins obtainable from Rohm and Haas. These resins catalyze a reaction involving the carbonyl compounds and converting them to materials which are lower boiling than phenol and thereby separatable from the phenol in a common distillation column. Great Britain No. 1,381,398 also separates the carbonyl impurities from the phenol composition wherein the phenol is substantially anhydrous by contacting the mixture with a solid acidic ion exchange resin insoluble in the mixture which converts the carbonyl containing impurities to products having boiling points higher than the boiling point of said phenol and distilling the phenol therefrom. Almost thirty years ago U.S. Pat. No. 3,029,294, hereinafter incorporated by reference, was applied for before the United States Patent Office. This patent removed the carbonyl contaminants from the phenol stream by contacting the carbonyl compounds with general catalyst including mineral acids, strong organic acids and solid surface active catalysts in order to convert the carbonyl compounds to substituted benzofurans by recondensing phenol with the carbonyl compounds and thereafter hydroextractively removing the benzofuran from the phenol as an overhead fraction. The organic acid is exemplified in U.S. Pat. No. 3,029,294 at column 2, lines 34-35 as a strong organic acid such as paratoluene sulfonic acid. It should be noted that all of these purification procedures start with a partially purified phenol made from the oxidation of cumene to the cumene hydroperoxide and then splitting the cumene hydroperoxide to phenol and acetone by a sulfuric acid catalyst system. These purification procedures disclosed and exemplified in the prior art references all use a new material not native to the general purification distillation procedures such as an ion exchange column or catalytically active materials such as alumina, mineral acids and montmorillonites, for example. Clearly such procedures are capital intensive and expensive operationally and can introduce further points for impurity contamination of the phenol and are outside the general utilized procedure.
It has now been discovered that these extraneous and expensive procedures for preparing a phenol purified from carbonyl contaminants are not necessary. Rather there is present in the phenol stream obtained from the initial distillation separation of acetone from phenol, native impurities, which if allowed to build to a critical concentration, can bring about a reaction between the carbonyl contaminant and phenol which thereby produces a compound which can readily be removed from the phenol by a procedure which is normally carried out in the recovery or in the purification procedures for phenol.
Current art-recognized phenol technology purifies the phenol fraction separated from the acetone fraction by a series of distillation towers. One of the towers is normally a "polishing" step for the phenol. Certain hydrocarbon or oil type materials are impurities carried along with the phenol stream. These hydrocarbon oil type impurities are removed from the phenol by a hydroextractive process. Introduced into a distillation tower is water to carry off the impurities from the phenol by an azeotroping or stream distillation technique. Also present in the column at this time are certain organic acid impurities. Up until this time these acid impurities are drawn off from the tower by side draws so as to not build up in concentrations since such organic acids would be corrosive to the ordinary tower material, stainless steel, at higher concentration.
We have surprisingly found that if these organic acid contaminants are allowed to build up in concentration, they reach a point where they catalyze a reaction between the carbonyl contaminants and the phenol thereby producing a compound which is readily removed by the hydroextractive steam distillation process already proceeding in the tower. The concentration of organic acids to the point which is catalytically active is also corrosive to the tower material. Such a build up of organic acids to the corrosive level is contrary to the teachings of the prior art. However, the production of the readily removable organic compound by hydroextraction techniques is clearly beneficial to the procedure since no extraneous materials need be added nor the phenol stream sidetracked to a specific ion exchange resin or any other technique for purging the phenol of the carbonyl contaminants. The reagents which catalyze the reaction are normally present in the phenol stream. Instead of removing them prior to the time they can catalyze the reaction, our invention allows them to build up to catalytic quantities. This concept had never been appreciated nor recognized in the prior art. This new process provides a low cost, highly efficient method for the further purification of phenol.